1. Field of the Invention
The present invention relates generally to cable television systems, and more particularly, to a cable television system wherein each subscriber can be individually addressed for determining which television signals the subscriber is authorized to receive.
2. Description of the Prior Art
Cable television systems are becoming increasingly popular, due in part to the fact that viewers are willing to pay a service fee for being able to receive special programs and features not available from networks that broadcast over the air waves. The relatively large number of channels which may be simultaneously transmitted over a cable television system allows for a wide variety of programming.
Not all subscribers are interested in or willing to pay for receiving all of the television programs on each of the transmitted channels. Accordingly, a desirable feature of a cable television system is the ability to provide subscribers with different levels of service for which correspondingly different service fees are charged. Apparatus is known for enabling particular subscribers to obtain basic cable service but prohibit reception of premium channel programs; however, such apparatus typically requires the installation of blocking filter devices at the home of the subscriber who does not wish to receive the premium channel programs. Apparatus of this type is expensive and is circumvented relatively easily by the subscriber. More sophisticated schemes for controlling reception of the premium channels involve electronically scrambling the composite television signal for making it unintelligible when received by subscribers who have not paid to have special descrambling equipment installed. Electronic scrambling, though effective, is expensive and degrades the quality of the received television signal. Cable television networks are sometimes used to transmit live coverage of certain one-time features, such as sporting events. If there were a convenient way for the operator of the cable television network to selectively allow requesting subscribers to access the special feature, then an additional premium could be charged to such requesting subscribers, including those subscribers who have already paid for receiving all normally available television programming.
When a subscriber falls behind in his payments for receiving cable television signals, the only means available to the cable television system operator for discontinuing service to the unpaying subscriber is to physically disconnect the coaxial drop cable that enters the subscriber's home from the cable television network. This procedure obviously requires that a service man be dispatched to the delinquent subscriber's home, at the expense of the cable television network operator.
Known cable systems typically offer a number of channels in excess of the twelve channels in the VHF wave band received by conventional television receivers. Accordingly, subscribers to cable television systems are often provided with a frequency converter for allowing their standard television receivers to utilize and present all of the channels transmitted on cable. The frequency converter is usually installed adjacent the subscriber's television receiver and is coupled between the drop cable entering the subscriber's home and the antenna of the television receiver. Because these frequency converters are located within the homes of the subscribers, the frequency converters are often subject to damage and even theft. Also, since the frequency converter is located within the subscriber's home, it is necessary to transmit television signals having relatively high carrier frequencies over the drop cable to the subscriber's home. Signal losses in the drop cable are significant at these higher frequencies and thereby limit the maximum practical length for which such drop cables may extend. Since the length of the drop cables must be kept relatively short, the number of distribution points along the cable at which such drop cables are coupled is relatively large.
Accordingly, it is an object of the present invention to provide a cable television system for transmitting a plurality of television signals and having a plurality of subscribers wherein the operator of the cable television system may conveniently and inexpensively control the television signals which may be received by each of the subscribers.
It is another object of the present invention to provide a cable television system which may be utilized to transmit premium television signals for which each subscriber must pay a premium in addition to his normal service fee and wherein the operator of the cable television system can conveniently and inexpensively allow subscribers who have paid the additional premium to receive the premium television signals.
It is still another object of the present invention to provide a cable television system wherein the frequency converter associated with each particular subscriber is in a secure location inaccessible by the subscriber or others.
It is a further object of the present invention to provide a cable television system wherein a plurality of such frequency converters can be disposed in a single secure location.
It is a still further object of the present invention to provide a cable television system which offers a relatively large number of different channels while avoiding the necessity to transmit relatively high carrier frequencies over drop cables extending to the subscriber's home.
It is yet another object of the present invention to provide a cable television system wherein the length of subscriber drop cables can be extended in order to minimize the number of subscriber distribution points along the cable.
It is still a further object of the present invention to provide a cable transmission system utilizing frequency converters for converting television signals transmitted by the cable to frequencies which may be utilized by the subscriber's television receiver wherein the frequency converters are located remote from the subscriber's home and wherein the power drain from the transmission cable is minimized when powering such remotely located frequency converters.
These and other objects of the present invention will become apparent to those skilled in the art as the description thereof proceeds.